1. Field of the Invention
The present invention relates to an acoustic apparatus.
2. Description of the Related Art
In an audio field for an electronic device which captures moving images or still images, an audio amplifier which receives a digital data signal in a bit stream format and outputs an analog signal is used. The audio amplifier can be used to output an audio signal recorded concurrently with imaging when playing the moving images, or a beep sound for informing a user that an operation button is pressed. In the audio amplifier, it is important not to output noise called pop noise from a loudspeaker when switching an operation state for outputting an audio signal and a non-operation state for not outputting the audio signal.
Japanese Patent Laid-Open No. 2005-45546 describes a digital amplifier circuit that prevents the pop noise from being output when outputting the beep sound. This digital amplifier circuit includes a speech processing circuit, a confirmation sound generation circuit for generating an operation confirmation sound signal, a reference signal generation circuit for generating a reference level signal, an addition circuit for adding the operation sound confirmation signal and the reference level signal, and a selection circuit for selecting one of the output of the speech processing circuit and that of the addition circuit. This reference signal processing circuit gradually changes the reference level signal from a power-off level to a reference level of the digital audio signal, or vice versa.
The digital amplifier circuit described in Japanese Patent Laid-Open No. 2005-45546 requires the reference signal generation circuit for gradually changing the reference level signal, and the addition circuit for adding the operation sound confirmation signal and the reference level signal. Hence, the digital amplifier circuit has a complicated arrangement.